Plasmids and mesosomes are unique to prokaryotic cells. Plasmids are small, double-stranded DNA molecules that can exist independently of the chromosome, and mesosomes are infoldings of the plasma membrane that aid in cellular processes like respiration. Prokaryotic cells lack a nuclear membrane; only eukaryotic cells have it. Ribosomes are present in both prokaryotic and eukaryotic cells, not unique to prokaryotes. Plasmids can also occur in some eukaryotes, therefore, the most appropriate option is and only.

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